A variety of different wireless video signal remote control systems are known. The most advanced of these was disclosed in U.S. Pat. No. 4,916,532, with aspects of the system being disclosed in U.S. Pat. Nos. 4,739,413, 4,697,893, 4,694,338 et. al. The system is mainly characterized by transmission of signal close to the ordinary TV signal, and frequency modulation to 902-928 MHz to provide clear and sharp display quality. However, the known system has the following defects:
(1) Its structure is sophisticated, and its production cost is relatively high;
(2) Frequency modulation makes transmission of two or more signals impossible at Federal Communications Commissions designated frequencies of 902-928 MHz because the bandwidth of each FM channel is very wide, and hence it is not possible to transmit signals in two different channels within a zone. Consequently, a channel for the second floor will interfere with a different channel for the third floor.
(3) The frequencies of 909 MHz and 921 MHz as proposed by the U.S. Pat. No. 4,916,532 result in a frequency shift at 909 MHz frequency modulation. With a bandwidth of 12 MHz, i.e., 903-915 MHz, a width of 1 MHz is reserved for 927 Mhz frequency modulation, but the shift for normal frequency modulation is at least 2-4 MHz for the best modulation effect. Hence overlapping occurs at the upper band and the lower band and mutual interference happens. Indeed, the cited patent is only useful in a channel within 902-928 MHz;
(4) Remote control signals and video signals fall in the same bandwidth, and it is difficult to separate these signals;
(5) Under the current technology level, with a bandwidth of 6 MHz, the frequencies mentioned in item (3) do not allow transmission to two or more audio video equipments in the same area at the designated frequency of 902-928 MHz simultaneously.
In view of the above defects, the inventor has created a wireless video/audio signal or data transmission device and its remote control circuit which has the following advantages:
(1) Video signals are transmitted by AM at 902-928 MHz;
(2) Remote control signals are sent by power line at above 100 KHz and below 20 MHz to eliminate interference from the power line at lower than 100 KHz and to minimize interference;
(3) Remote control signals can be sent by either AM or FM, as desired by an individual client. A remote control signal is received by the video signal reception side. It is an infrared signal, which is detected and modulated (AM or FM) to 100 KHz-20 MHz, and then transmitted to the video signal transmitter side via a power line. The remote control signal is then demodulated (AM or FM), sent to the main control of the video signal transmitter side, or converted to an infrared signal to control its peripheral such as a TV, VCR, CATV converter, or other device which can be controlled by an infrared signal. Because the signal is modulated to the band of 100 KHz-20 MHz which can prevent interference, the present invention is different from that disclosed by U.S. Pat. No. 4,509,211, which detects a remote control infrared signal directly, sends the signal through a wire without modulation, and amplifies the signal to drive an IR diode directly. The present invention is also different from that disclosed by the U.S. Pat. No. 4,809,359 which applied radio signals for control of a device.
(4) There is a great difference in frequency between the video signal and the remote control signal and different media are used to carry these signals, hence interference is minimized, and the separate carriers lower production cost.
(5) The video signal is transmitted by AM, hence two or more channels can be used in the FCC band 902-928 MHz without mutual interference.
(6) There is an automatic gain control (AGC) to provide a stable and appropriate output to meet Federal Communication Commission requirements.